Optical waveguide device integrated module and method of manufacturing the same

ABSTRACT

A semiconductor laser and an optical waveguide device with an optical waveguide formed at a surface of its substrate are provided on a submount. The semiconductor laser and the optical waveguide device are mounted with an active layer and a surface at which the optical waveguide is formed facing the submount, respectively. The submount is combined with the semiconductor laser or the optical waveguide device to form one body using an adhesive with a spacer, which maintains a substantially uniform distance therebetween, being interposed therebetween, so that position adjustment in the height direction can be made automatically and mounting can be carried out with high-precision optical coupling. Thus, an optical waveguide device integrated module and a method of manufacturing the same are provided, in which a semiconductor laser and a planar optical waveguide device are mounted with their positions in the height direction controlled with high precision.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an optical waveguide deviceintegrated module with a semiconductor laser and an optical waveguidedevice that are mounted on a submount and to a method of manufacturingthe same.

2. Related Background Art

In the optical communication field, it is considered important todevelop a hybrid integrated optical module including a semiconductorlaser, an electronic element, an optical fiber, and the like that areintegrated on a quartz-based lightwave circuit platform. This is anindispensable technique for reducing the size and cost of modules. Inthe technique, it is important to fix each element with high precisionto minimize transfer-loss.

A surface mounting optical module has been proposed in which asemiconductor laser and a single mode fiber are bonded directly using aV-groove groove Si substrate (IEICE (The Institute of Electronics,Information and Communication Engineers) Conference 1997, C-3-63). FIG.12 shows a structural view. Alignment keys 26 are formed in a Sisubstrate 24 and a semiconductor laser 25. The alignment keys 26 aresubjected to image recognition, so that the center of a V-groove 27 anda position of an emission point of the semiconductor laser 25 aredetected. Thus, position adjustment is carried out with high precision.Mounting variations of about ±0.61 μm in the x direction and about ±1 μmin the z direction are achieved with respect to the V-groove 27 of theSi substrate 24. An optical fiber 28 is mounted in the V-groove 27accurately. The V-groove 27 is formed with high precision by anisotropicetching of Si. Similarly, the optical fiber 28 is produced with itsouter dimension and core center controlled with high precision.Therefore, the fiber 28 is fitted into and is fixed to the V-groove 27,so that the optical fiber 28 can be fixed with respect to thesemiconductor laser 25 with high precision.

On the other hand, in order to achieve the increases in density ofoptical disks and in definition of a display, a small short-wavelengthlight source is required. Techniques for obtaining short wavelengthlight include blue light generation using a semiconductor laser and anoptical waveguide second harmonic generation (hereinafter referred to as“SHG”) device employing a quasi-phase-matched (hereinafter referred toas “QPM”) system (Yamamoto et al., Optics Letters Vol. 16, No. 15,p1156, (1991)).

FIG. 13 shows a schematic structural view of a blue light source usingan optical waveguide QPM-SHG device. A wavelength variable semiconductorlaser having a distributed Bragg reflector (hereinafter referred to as“DBR”) region (hereinafter referred to as a “wavelength-variable DBRsemiconductor laser”) is used as a semiconductor laser. Numeral 29 is a100-mW class AlGaAs-based wavelength-variable DBR semiconductor laser ina 0.85-μm range. The semiconductor laser includes an active layer regionand a DBR region. An amount of current applied to the DBR region isvaried, so that the emission wavelength can be varied.

An optical waveguide QPM-SHG device 30 as a wavelength conversion deviceincludes an optical waveguide and a region whose polarization isreversed periodically, which are formed on a x-cut Mg-doped LiNbO₃substrate. A SiO₂ protective film 31 is formed on the surface at whichthe optical waveguide is formed. The wavelength-variable DBRsemiconductor laser 29 and the optical waveguide QPM-SHG device 30 arefixed so that the active layer and the surface at which the opticalwaveguide is formed are in contact with a submount 32, respectively(hereinafter referred to as “face down mounting”). A laser beam obtainedfrom an emission surface (from which a beam leaves the laser 29) of thewavelength-variable DBR semiconductor laser 29 is coupled directly tothe optical waveguide of the optical waveguide QPM-SHG device 30.

The optical coupling adjustment is carried out with the semiconductorlaser emitting a beam, and with respect to a 100-mW laser output, a60-mW laser beam was coupled to the optical waveguide. The amount ofcurrent applied to the DBR region of the wavelength-variable DBRsemiconductor laser is controlled and thus the emission wavelength isset within a tolerance of the phase matched wavelength of the opticalwaveguide QPM-SHG device. Currently, about 10-mW blue light with awavelength of 425 nm has been obtained.

In an optical module in which a semiconductor laser and an optical fiberare integrated, the optical fiber is mounted in a V-groove formed in aSi submount and the semiconductor laser is mounted using the V-groove asa reference position. The optical fiber has a cylindrical shape and hasa core portion (an optical propagation region) formed in its center. Theoptical fiber is formed with its diameter controlled with highprecision. In addition, the V-groove in the Si submount also is formedwith high precision using the anisotropic etching of Si. Therefore, theoptical fiber is mounted with its core portion as the center of theoptical fiber being adjusted with respect to the Si submount with highprecision. On the other hand, the alignment keys used for positioningthe semiconductor laser also are formed in reference to the V-groove andtherefore the semiconductor laser also can be mounted with highaccuracy.

In a planar optical waveguide device with an optical waveguide formed ona surface of a LiNbO₃ substrate by proton exchange or Ti diffusion(devices other than optical waveguide devices with an optical waveguidelayer (core) in the coaxial center like an optical fiber are referred toas “planar optical waveguide devices” in the present invention), thedistance from the substrate surface to the optical waveguide iscontrolled with high precision. In an integrated module including asemiconductor laser and a planar optical waveguide device, thesemiconductor laser is fixed with a solder material and the opticalwaveguide device is fixed with an adhesive by face down mounting. In thesemiconductor laser, generally, an active layer is formed on an n-typesubstrate, and a P-type clad layer and further a p-side electrode areformed thereon. Therefore, the distance from the p-side surface to theactive layer is about 3 μm. The solder material has a thickness of about1 to 2 μm. Consequently, the distance from the submount to the activelayer after mounting is about 4 to 5 μm. This distance can be controlledto be about ±0.2 μm through the adjustment of the amount of pressureapplied to the semiconductor laser during the mounting.

On the other hand, since the optical waveguide portion of the planaroptical waveguide device is formed at the substrate surface, thedistance from the substrate to the optical waveguide portion is about 1μm. Therefore, there is a difference in level of about 3 to 4 μm betweenthe active layer of the semiconductor laser and the optical waveguideportion of the optical waveguide device. Consequently, it has beendifficult to carry out the adjustment without allowing the semiconductorlaser to emit a beam (hereinafter referred to as “passive alignmentmounting”).

A method has been proposed in which a thick film is formed on a planaroptical waveguide device to allow the levels of an active layer of asemiconductor laser and an optical waveguide portion of the planaroptical waveguide device to coincide with each other. This method,however, has the following problems.

(1) Conditions for manufacturing the optical waveguide vary due to theincrease in temperature of a substrate during the formation of the thickfilm. Particularly, in the case of a SHG device employing the QPMsystem, a phase matched wavelength may vary and the wavelengthconversion characteristics may deteriorate with the variation inrefractive index of the optical waveguide.

(2) After being formed, the thick film shrinks and therefore, asubstrate may warp. The warping makes it difficult to mount the deviceon a submount.

(3) The thick film has a thickness of about several micrometers.Therefore, it is difficult to control the thickness to be uniform.

(4) In fixing the optical waveguide device with an adhesive, when thethickness of the adhesive is not uniform, heat from the submount cannotbe conducted uniformly. Therefore, particularly in the wavelengthconversion device employing the QPM system, the phase matched wavelengthmay vary or the wavelength conversion characteristics may deteriorate.

On the other hand, in the adjustment of optical coupling between thesemiconductor laser and the planar optical waveguide device in the widthdirection, conventionally, an adhesive was applied after the opticalcoupling adjustment and then was dried to fix them. Therefore,misalignment after the adjustment might be caused by the stress exertedduring the application of the adhesive or the shrinkage of the adhesiveupon curing.

In the optical waveguide QPM-SHG device utilizing the second harmonicgeneration, the power of harmonic light obtained is proportional to thesquare of the power of a fundamental wave to be coupled. Therefore, itis indispensable to improve the coupling efficiency and reduce thevariations among samples.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to solve theabove-mentioned problems and to provide an optical waveguide deviceintegrated module in which a semiconductor laser and a planar opticalwaveguide device are mounted with their positions in their heightdirection controlled with high precision and to provide a mountingmethod for manufacturing the same.

In order to achieve the aforementioned object, an optical waveguidedevice integrated module according to the present invention includes asemiconductor laser and an optical waveguide device on a submount. Theoptical waveguide device includes an optical waveguide formed on asurface of its substrate. The semiconductor laser and the opticalwaveguide device are mounted on the submount with both a surface of thesemiconductor laser at which an active layer is formed and a surface ofthe optical waveguide device at which the optical waveguide is formedfacing the submount. The submount is combined with the semiconductorlaser or the optical waveguide device to form one body using an adhesivewith a spacer being interposed therebetween. The spacer maintains asubstantially uniform distance between the submount and thesemiconductor laser or the optical waveguide device.

A mounting method for manufacturing an optical waveguide deviceintegrated module according to the present invention is directed to amounting method for manufacturing an optical waveguide device integratedmodule including a semiconductor laser and an optical waveguide devicemounted on a submount with both a surface of the semiconductor laser atwhich an active layer is formed and a surface of the optical waveguidedevice at which an optical waveguide is formed facing the submount. Themethod includes mounting at least one of the semiconductor laser and theoptical waveguide device on the submount with an adhesive, with a spacerbetween the submount and the semiconductor laser or the opticalwaveguide device. The spacer maintains a substantially uniform distancebetween the submount and the semiconductor laser or the opticalwaveguide device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural view of a SHG blue light source according to afirst embodiment of the present invention.

FIG. 2 is a diagram indicating a waveguide mode with respect to afundamental wave of an optical waveguide QPM-SHG device according to thefirst embodiment of the present invention.

FIG. 3 is a graph showing variations in maximum optical couplingefficiency in coupling between an emission mode of a semiconductor laserand a waveguide mode of the optical waveguide QPM-SHG device accordingto the first embodiment of the present invention when the diameter of aglass bead is changed.

FIG. 4 is an explanatory drawing of a ridge QPM-SHG device according tothe first embodiment of the present invention.

FIGS. 5A to 5D are assembly drawings of the SHG blue light sourceaccording to the first embodiment of the present invention.

FIGS. 6A to 6C are drawings explaining load positions according to thefirst embodiment of the present invention.

FIGS. 7A and 7B are drawings explaining a mounting method usingcylindrical bodies according to the first embodiment of the presentinvention.

FIGS. 8A to 8D are assembly drawings of a SHG blue light sourceaccording to a second embodiment of the present invention.

FIGS. 9A to 9C are assembly drawings of a SHG blue light sourceaccording to a third embodiment of the present invention.

FIG. 10 is a graph showing the moving accuracy and viscosity of anultraviolet curing agent according to the third embodiment of thepresent invention.

FIG. 11 is a structural view of a SHG blue light source according to afourth embodiment of the present invention.

FIG. 12 is a structural view of a surface mounting optical moduleobtained by direct bonding according to a conventional example.

FIG. 13 is a structural view of a direct-bonding SHG blue light sourceaccording to a conventional example.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a spacer is used that can maintain asubstantially uniform distance between the submount and thesemiconductor laser or the optical waveguide device when pressure isapplied during the mounting. In this context, the “substantially uniformdistance” denotes a distance, preferably, within a variation range ofabout 10%. A spacer with a regular shape such as a spherical orcylindrical shape can be used preferably.

In the present invention, it is preferable that the distance from thesubmount surface to the optical waveguide is adjusted depending on asize of the spherical or cylindrical body so that a maximum couplingefficiency is obtained in coupling a beam emitted from the semiconductorlaser to the optical waveguide.

It is preferable that a plurality of spherical or cylindrical bodies arepresent.

Preferably, the spherical or cylindrical bodies are arranged in a singlelayer between the submount and the optical waveguide device or thesemiconductor laser. In this specification, the description that “thespherical or cylindrical bodies are arranged in a single layer” denotesthat the respective spherical or cylindrical bodies are arranged so asnot to overlie on top of another.

Preferably, the spherical or cylindrical body is mixed with an adhesivein the semiconductor laser.

It is preferable that an amount of the spherical or cylindrical bodiesmixed with the adhesive is not more than 30 vol. %, further preferablyin the range of 0.1 vol. % to 20 vol. %.

Preferably, the spherical or cylindrical bodies have substantially thesame size. In this context, the term “substantially” denotes that theirsizes may differ from one another slightly, and specifically, adifference of ±10% is allowable.

Preferably, the optical waveguide device is a quasi-phase-matchedwavelength conversion device with a region whose polarization isreversed periodically.

In addition, it is preferable that the spherical or cylindrical body isformed of at least one material selected from a group consisting ofglass materials, resins such as acrylic resin,polydivinylbenzene-containing resin, formaldehyde condensate resin andthe like, and ceramics.

Preferably, the adhesive in the optical waveguide device has been curedby irradiation of ultraviolet rays.

Preferably, the adhesive used for fixing the semiconductor laser is asolder or a conductive adhesive.

Preferably, the spherical body has a mean grain size of not more than 10μm, further preferably in a range of 1 μm to 9 μm.

Preferably, the cylindrical body has a mean length of 10 μm to 100 μm.

Furthermore, it is preferable that a relationship of d₁+d₂+Δ≅d₃+d₄ issatisfied, where d₁ denotes a diameter of the spherical or cylindricalbody, d₂ a distance from the surface of the optical waveguide device toa position where an intensity of a laser beam waveguide mode of theoptical waveguide reaches its peak, d₃ a distance from the surface ofthe semiconductor laser at which the active layer is formed to aposition where an intensity of a laser beam emitted from thesemiconductor laser reaches its peak, d₄ a thickness of the adhesiveused for mounting the semiconductor laser on the submount, and Δ adistance between the position where an intensity of a laser beamwaveguide mode of the optical waveguide reaches its peak and a positionwhere a maximum optical coupling efficiency is obtained in coupling abeam emitted from the semiconductor laser to the optical waveguide.

It also is preferable that Δ≅0 and Δ=α a when the laser beam waveguidemode of the optical waveguide has a symmetric shape and an asymmetricshape with respect to the direction of a thickness of the substrate,where α denotes the distance between the position where an intensity ofa laser beam waveguide mode of the optical waveguide reaches its peakand the position where a maximum optical coupling efficiency is obtainedin coupling a beam emitted from the semiconductor laser to the opticalwaveguide.

In the mounting method according to the present invention, it ispreferable that an optical coupling adjustment in the optical waveguidedevice is carried out with the semiconductor laser emitting a beam.

Preferably, the adhesive is ultraviolet curable resin that is cured byirradiation of ultraviolet rays. Ultraviolet curable resins that can beused in the present invention include those prepared by mixing, forexample, acrylic monomer, oligomer (such as polyester-, polyurethane-,or epoxy-acrylic ester with a molecular weight of about 1000 to 5000, orthe like), a photoinitiator (benzophenone, benzoin ethyl ether, or thelike), and a polymerization inhibitor.

In the mounting method of the present invention, it is preferable thatthe adhesive is applied to the submount, an adjustment in opticalcoupling between the semiconductor laser and the optical waveguidedevice is carried out with the adhesive being present between theoptical waveguide device and the submount, and then the opticalwaveguide device is fixed.

Preferably, the adhesive has a viscosity of not more than 100 cps.

It also is preferable that a center position of a load applied inmounting the optical waveguide device or the semiconductor laser on thesubmount is: in the vicinity of the spherical or cylindrical bodies whenthe spherical or cylindrical bodies are positioned in one place; on aline extending between two points when the spherical or cylindricalbodies are positioned in two places; or inside a region defined by linesextending between three points or more when the spherical or cylindricalbodies are positioned in three places or more; and on the opticalwaveguide device or the semiconductor laser.

Preferably, the area of a portion of a jig used in mounting the opticalwaveguide device or the semiconductor laser on the submount coming intocontact with the optical waveguide device or the semiconductor laser issmaller than the area of the optical waveguide device or thesemiconductor laser.

Preferably, at least one of the optical waveguide device and thesemiconductor laser is mounted on the submount while a load is appliedto the at least one. Particularly, it is preferable that the loadapplied to the optical waveguide device is not more than 500 g.

Preferably, the spherical or cylindrical body is mixed with theadhesive.

It also is preferable that a ratio of the spherical or cylindricalbodies mixed with the adhesive is not more than 30 vol. %.

Preferably, the position of the optical waveguide device is adjustedwith the semiconductor laser emitting a beam and then the opticalwaveguide device is mounted on the submount.

Preferably, the spherical or cylindrical bodies have substantially thesame size. In this context, the term “substantially” denotes that theirsizes may differ from one another slightly, and specifically, adifference of ±10% is allowable.

It is desirable that the adhesive used for fixing the semiconductorlaser is a solder or a conductive adhesive.

In the optical waveguide device integrated module in which asemiconductor laser and a planar optical waveguide device areintegrated, it is important to improve the coupling efficiency and toreduce the variations in the coupling efficiency among samples.Particularly, in a short-wavelength light source including asemiconductor laser and an optical waveguide QPM-SHG device, a power ofharmonic light obtained is proportional to the square of a power of thefundamental wave to be coupled. Therefore, the improvement in thecoupling efficiency and the reduction of the variations in the couplingefficiency among samples are particularly important factors. The moduleand mounting method according to the present invention can satisfy suchimportant factors.

As described above, the present invention allows levels of the activelayer of the semiconductor laser and the optical waveguide of theoptical waveguide device to coincide with each other automatically. Inaddition, even when the adhesive shrinks upon being cured, it has lessinfluence on the decrease in the coupling efficiency since thepositioning in the height direction is made by the spherical orcylindrical bodies.

According to the mounting method of the present invention, the timerequired for mounting can be shortened. In addition, when the sphericalor cylindrical bodies are mixed with an adhesive, the levels of theactive layer of the semiconductor laser and the optical waveguide of theoptical waveguide device are allowed to coincide with each otherautomatically. In addition, even when the adhesive shrinks upon beingcured, it has less influence on the decrease in the coupling efficiencysince the positioning in the height direction is made by the sphericalor cylindrical bodies.

In the following embodiments, the descriptions are directed to a methodof achieving high-efficiency optical coupling by controlling thethicknesses of an optical waveguide and an active layer with highprecision in an optical waveguide device integrated module including asemiconductor laser and a planar optical waveguide device.

First Embodiment

In the present embodiment, the description is directed to a SHG bluelight source with an optical waveguide quasi-phase-matched secondharmonic generation (QPM-SHG) device as a planar optical waveguidedevice and a wavelength-variable DBR semiconductor laser as asemiconductor laser. The optical waveguide QPM-SHG device is produced ona Mg-doped LiNbO₃ substrate. The DBR semiconductor laser has awavelength varying function.

In the present embodiment, spherical or cylindrical bodies are placedbetween the planar optical waveguide device and a submount, so that theposition in the height direction of an optical waveguide in the planaroptical waveguide device is controlled with high precision. Thus,high-efficiency optical coupling is achieved.

FIG. 1 shows a drawing illustrating the configuration of the SHG bluelight source according to the present embodiment. The SHG blue lightsource includes an optical waveguide QPM-SHG device 2 and awavelength-variable DBR semiconductor laser 3, which are mounted on a Sisubmount 4. The SHG device 2 includes a proton exchange opticalwaveguide 5 and a region 6 whose polarization is reversed periodically(hereinafter referred to as a “polarization reversed region”), which areformed on an x-cut Mg-doped LiNbO₃ substrate 1. The polarizationreversed region 6 is produced by formation of a comb-shaped electrode onthe +x plane of the LiNbO₃ substrate and application of an electricfield. The difference in propagation velocity between fundamentalwavelength light and second harmonic light is corrected by thepolarization reversed region. Thus, a quasi phase matched condition issatisfied. A fundamental wave and a harmonic wave propagate in theproton exchange optical waveguide 5 as guided waves. Therefore, a longdistance for interaction can be secured and thus high exchangeefficiency can be achieved.

A SiO₂ protective film 7 (with a thickness of 200 nm) is formed on theproton exchange optical waveguide 5. FIG. 2 shows a waveguide mode ofthe fundamental wave. The fundamental wave had a full width at halfmaximum of 3 μm with respect to the thickness (height) direction and adistance from the substrate surface to a position where the intensity ofthe waveguide mode reached its peak was 2 μm.

The DBR semiconductor laser 3 is an AlGaAs-based semiconductor laser andhas an emission wavelength of 820 nm. The semiconductor laser 3 includesan active region (an active layer) 8 and a DBR (distributed Braggreflector) region 9 with diffraction gratings formed therein. Light fromthe DBR region 9 corresponding to the pitch of the diffraction gratingenters to and is fed back from the active layer 8 and resonates betweenthe end face of the active region 8 from which light leaves and the DBRregion 9. The emission wavelength is set to be the wavelength of thelight fed back from the active layer (hereinafter referred to as a“feedback wavelength”). In the DBR region 9, an internal heater isprovided. Current application to the internal hater allows therefractive index of the diffraction grating of the DBR region 9 to vary.This can vary the feedback wavelength and thus the emission wavelength.A wavelength variable range of 2 nm is achieved.

An n-type clad layer and an active layer are formed on an n-type GaAssubstrate, and a p-type clad layer and further a p-side electrode wereformed thereon. The distance from the p-side surface (i.e. the surfaceat which the active layer was formed) to an emission center was 3 μm.

On the Si submount, a Ti/Pt/Au metallization film is formed, and a Pb/Snsolder 10 is provided, by vapor deposition, in a portion on which thesemiconductor laser is to be mounted. The solder material has athickness of 3 μm. The amount of pressure applied to the DBRsemiconductor laser during mounting was adjusted, so that the thicknessof the solder material after fixing was set to be 2 μm. As a result, thedistance from the Si submount 4 to the emission center (i.e. a positionwhere the intensity of an emitted laser beam reaches its peak) after themounting was 5 μm.

As described above, the emission center of the semiconductor laser islocated 5 μm apart from the Si submount in the height direction. On theother hand, the distance from the surface of the substrate of the SHGdevice 2 to the position where the intensity of the waveguide modereaches its peak is 2 μm. Therefore, it is necessary for opticalcoupling with high efficiency to adjust the position in the heightdirection of the SHG device 2. In the present embodiment, sphericalglass beads 11 are interposed between the SHG device 2 and the Sisubmount 4, so that the thickness is adjusted. The variation in meangrain size of the glass beads 11 is not more than ±0.1 μm, and thisenables position adjustment in the height direction with high precision.Practically, the size of the spherical glass beads 11 was determined sothat the maximum optical coupling efficiency in coupling between thewaveguide mode of the SHG device 2 and the emission mode of thesemiconductor laser was obtained.

The method of determining the size of the spherical glass beads 11 isdescribed in detail as follows. Suppose the diameter of spherical orcylindrical bodies is indicated as d₁, the distance from the surface ofthe optical waveguide QPM-SHG device to the position where the intensityof the laser optical waveguide mode of the optical waveguide reaches itspeak as d₂ (FIG. 2), the distance from the surface of the semiconductorlaser at which the active layer is formed to the position of the activelayer (i.e. the distance corresponding to half the thickness of theactive layer) as d₃ (FIG. 1), and the thickness of the solder film usedfor mounting the semiconductor laser on the submount as d₄ (FIG. 1). Inthe present embodiment, d₂=2 μm, d₃=3 μm, and d₄=2 μm. In this case, themaximum optical coupling efficiency in coupling between the waveguidemode of the SHG device 2 and the emission mode of the semiconductorlaser cannot always be obtained merely by using the glass beads 11 witha diameter d₁ of 3 μm so that the relationship of d₁+d₂≅d₃+d₄ issatisfied. As shown in FIG. 2, the laser beam waveguide mode of theoptical waveguide in the SHG device used in the present embodiment isasymmetric with respect to the intensity peak. When the laser beamwaveguide mode is asymmetric with respect to the intensity peak as inthis case, the distance from the surface of the SHG device to theposition where the maximum optical coupling efficiency in couplingbetween the laser beam waveguide mode of the optical waveguide and theemission mode of the semiconductor laser is obtained is d₂+Δ.

FIG. 3 shows the variation in maximum optical coupling efficiency in thecoupling between the emission mode of the semiconductor laser and thewaveguide mode of the SHG device 2 when the diameter d₁ of the glassbeads 11 is changed. As shown in FIG. 3, when the glass beads 11 have adiameter d₁ of 2.7 μm, the maximum optical coupling efficiency wasobtained. From the result described above, since d₁=2.7 μm, d₂=2 μm,d₃=3 μm, and d₄=2 μm, Δ≅0.3 μm when the relationship of d₁+d₂+Δ≅d₃+d₄ issatisfied In this case, a maximum optical coupling efficiency can beobtained.

The present embodiment employs the optical waveguide device in which thelaser beam waveguide mode of the optical waveguide is asymmetric withrespect to the intensity peak. However, when the laser beam waveguidemode of the optical waveguide is symmetric with respect to the intensitypeak, Δ≅0 holds. For instance, when a ridge QPM-SHG device 35 as shownin FIG. 4 is produced, the laser beam waveguide mode of an opticalwaveguide 36 is symmetric with respect to the intensity peak.

In the present embodiment, glass beads were used as the sphericalbodies. Besides the glass material, however, even when using acrylicresin, polydivinylbenzene-containing resin material, formaldehydecondensate resin, or ceramics as the material of the spherical bodies,spherical bodies with the same grain size precision as that of the glassbeads can be obtained and the position control in the height directionalso can be achieved with high precision. However, when the grain sizeof the spherical bodies exceeds 10 μm, it becomes difficult to producethe spherical bodies and their grain size precision may deteriorate.Therefore, in order to achieve the position control in the heightdirection with high precision, preferably, spherical bodies with a grainsize of not more than 10 μm are used.

A mounting method of the present invention is described with referenceto FIGS. 5A to 5D. First, a plurality of glass beads 11 with a meangrain diameter (φ) of 2.7 μm were applied to the surface of the SHGdevice 2 at which the optical waveguide was formed (hereinafter referredto as an “optical waveguide formation surface”). As the applicationmethod, a method was employed that included mixing a plurality of glassbeads 11 with acetone, stirring well, and applying a trace amount of themixture to the optical waveguide formation surface. The acetone wasevaporated and thus a layer with glass beads 11 dispersed on the opticalwaveguide formation surface was formed. When using such a method, asingle layer of the glass beads 11 can be formed and thus the positionadjustment in the height direction can be carried out with higherprecision. In the present embodiment, the glass beads 11 were applied tothe SHG device 2. However, no problem was caused even when the glassbeads 11 were applied to the Si submount 4.

As shown in FIG. 5B, optical coupling adjustment was carried out whilethe semiconductor laser was allowed to emit a beam. The SHG device 2 wasplaced on the Si submount 4 on which the DBR semiconductor laser 3 hadbeen mounted. The SHG device was fixed to a vacuum pincette and wasmoved for the adjustment. In the present embodiment, since the positionadjustment in the height direction automatically was made by the glassbeads 11, the adjustments were carried out with respect to an opticalaxis direction X and a width direction (a direction perpendicular to theoptical axis direction X) Y. The distance between the opposed ends ofthe semiconductor laser and the SHG device was set to be 3 μm. Then, theposition adjustment in the width direction Y was carried out so that apeak output of the laser beam obtained from the emission end face of theoptical waveguide can be obtained while the semiconductor laser and theSHG device were moved relative to each other in the width direction Y.Thus, the position adjustments in the optical axis direction X and thewidth direction Y were completed.

In order to fix the SHG device 2, the SHG device 2 was moved upward inthe direction perpendicular to the Si submount 4. Then, an ultravioletcurable agent 12 was applied to the Si submount 4 with the DBRsemiconductor laser 3 mounted thereon (FIG. 5C). In the presentembodiment, an epoxy-based adhesive obtained by cationic polymerizationwas used and its viscosity was about 1000 cps. Afterward, the SHG device2 was moved downward in the direction perpendicular to the Si submount 4and was placed in a position where the peak output was obtained whilethe semiconductor laser was allowed to emit a beam. Then, an irradiationof ultraviolet lays were carried out for about 30 seconds while a loadwas applied to the SHG device 2. Thus, the SHG device 2 was fixed (FIG.5D). It is necessary to apply a load to the SHG device 2 to arrange theglass beads 11 in a single layer. However, when the mounting is carriedout under a load set to be 500 g or more, the SHG device 2 may bedamaged in some cases. Therefore, it is desirable that the load appliedto the SHG device 2 is not more than 500 g.

In order to control the gap between the Si submount 4 and the SHG device2 with high precision, attention also should be paid to the positionwhere the load is applied. In order to control the gap between the Sisubmount 4 and the SHG device 2 with high precision, the load isrequired to be applied to a position located in the vicinity of thecenter of a region where the glass beads 11 are placed and on the SHGdevice 2 as shown in FIG. 6A. When the glass beads 11 are positioned inone place in a gathered state as shown in FIG. 6A, a load may be appliedto the vicinity of the point X shown in the figure located on the SHGdevice 2 and inside the region where the glass beads are placed. Whenthe load center is located at a point Y or Z, the SHG device 2 cannot bemounted in parallel to the Si submount 4. This results in the gapbetween the Si submount 4 and the SHG device 2 not being controlled withhigh precision. When the glass beads 11 are divided to be placed in afew places (four places in FIG. 6B) as shown in FIG. 6B, the region inwhich the glass beads are placed is defined as indicated by the brokenline in the figure. Similarly in this case, it is required to apply aload to the vicinity of the point X′ located on the SHG device 2 and inthe vicinity of the center of the region where the glass beads 11 areplaced.

Furthermore, attention also should be paid to the size of a jig used forapplying the load to the SHG device 2. In the present embodiment, theload was applied to the SHG device 2 using a vacuum pincette. When thearea of a portion of a jig 38 for applying a load coming into contactwith the SHG device 2 is smaller than the area of the SHG device 2 asshown in FIG. 6C, it is easy to apply the load to the point X shown inFIG. 6A or the point X′ shown in FIG. 6B located on the SHG device 2 andinside the region where the glass beads are placed. When the area of aportion, of the jig 38 for applying a load, coming into contact with theSHG device 2 is larger than the area of the SHG device 2, not only mayit be difficult to apply the load to the point X shown in FIG. 6A or thepoint X′ shown in FIG. 6B located on the SHG device 2 and inside theregion where the glass beads are placed, but also ultraviolet rays withwhich the ultraviolet curable agent 12 is to be irradiated are blocked.This results in defective fixing of the SHG device 2 to the Si submount4. For the reason described above, it is preferable that the area of aportion of the jig for applying a load to the SHG device 2 coming intocontact with the SHG device 2 is smaller than the area of the SHG device2.

With respect to a 50-mW semiconductor laser output, a 25-mW laser beamwas coupled to the optical waveguide. The wavelength of the DBRsemiconductor laser 3 was allowed to coincide with the phase matchedwavelength of the SHG device, so that 3-mW blue light with a wavelengthof 410 nm was obtained.

Generally, the adhesive shrinks upon being cured. Therefore, when theadhesive is cured after the optical coupling adjustment, the opticalcoupling efficiency at the time of the adjustment differs from thatafter fixing. In the present embodiment, however, glass beads arepresent between the SHG device and the Si submount. Therefore, themisalignment in the height direction is not caused even when theadhesive shrinks upon being cured. Thus, the configuration of thepresent embodiment has a significant practical effect.

The ultraviolet curable agent can be cured by irradiation of ultravioletrays. Therefore, the SHG device can be fixed in a short time byirradiation of ultraviolet rays after the optical coupling adjustment.Consequently, stable fixing is achieved. In the case of using athermosetting adhesive or the like, a shift in the position determinedby the optical coupling adjustment may occur during heating. Therefore,the ultraviolet curable agent is a preferable adhesive in a method inwhich an optical coupling adjustment is carried out while asemiconductor laser is allowed to emit a beam as in the presentembodiment (hereinafter referred to as an “active alignment mounting”).Furthermore, in the substrate for a wavelength conversion deviceintended to generate blue light such as the Mg-doped LiNbO₃ substrate,since light in a wavelength range up to about 300 nm is transparent, theultraviolet curable agent is a preferable adhesive.

In the present embodiment, spherical glass beads were used. However, thesame effect also can be obtained in the case of using fiber-like(cylindrical) bodies. Furthermore, their diameter can be adjusted withhigher precision and therefore the fiber-like bodies are preferable. Inthis case, when using cylindrical bodies with a length of 100 μm orlonger, the cylindrical bodies 34 tend to overlie one on top of anotheras shown in FIG. 7A, since they are too long. Consequently, it isdifficult to arrange them in a single layer. On the other hand, when thecylindrical bodies have lengths not more than 10 μm, the cylindricalbodies may stand. This may deteriorate the precision of the gap betweenthe Si submount 4 and the SHG device 2. For the reason described above,it is desirable that the cylindrical bodies have a mean length of 10 μmto 100 μm.

In the present embodiment, the glass beads were used for the adjustmentin the height direction. Glass has poor thermal conductivity. For theoptical waveguide QPM-SHG device, it is important to have temperatureuniformity since the phase matching is satisfied by periodicalpolarization reversal. The heat generated by the semiconductor laser istransmitted through the Si submount and causes nonuniformity in thetemperature of the SHG device. When the glass beads with low thermalconductivity are interposed as in the present embodiment, the uniformityin temperature of the SHG device can be maintained. Therefore,high-efficiency wavelength conversion can be achieved. This provides asignificant effect.

In the present embodiment, the optical waveguide quasi-phase-matchedsecond harmonic generation (QPM-SHG) device produced on a Mg-dopedLiNbO₃ substrate was used as a planar optical waveguide device. In sucha blue light source, the power of the blue light obtained isproportional to the square of the power of a fundamental wave to becoupled. Therefore, the improvement in optical coupling efficiency isparticularly important. The configuration of the present embodimentcapable of obtaining highly stable optical coupling characteristics is apractical means and provides a significant effect. In addition, sincethe Si submount and the SHG device are not in direct contact due to thepresence of the spherical or cylindrical bodies, the influence of theheat generation by the semiconductor laser is considerably small.Therefore, the uniformity in temperature is maintained in the SHGdevice. This provides a significant practical effect.

Second Embodiment

In the present embodiment, a planar optical waveguide device is fixed toa submount using an adhesive with spherical or cylindrical bodies mixedtherein and the position in the height direction of an optical waveguidein the planar optical waveguide device is controlled with highprecision. Thus, high-efficiency optical coupling is achieved. Similarlyin the present embodiment, the description is directed to a SHG bluelight source with an optical waveguide quasi-phase-matched secondharmonic generation (QPM-SHG) device as a planar optical waveguidedevice and a wavelength-variable DBR semiconductor laser as asemiconductor laser. The optical waveguide QPM-SHG device is produced ona Mg-doped LiNbO₃ substrate. The DBR semiconductor laser has awavelength varying function.

As described in the first embodiment, the distance from the Si submountto an emission center of the semiconductor laser is 5 μm. The waveguidemode of a fundamental wave in the SHG device had a full width at halfmaximum of 3 μm with respect to a thickness direction. The distance fromthe substrate surface to a position where the intensity of thetransverse mode reached its peak was 2 μm. In order to achieve opticalcoupling with high efficiency, it is required to adjust the position ofthe SHG device in the height direction. As in the first embodiment, thesize of spherical glass beads 11 was determined so that a maximumoptical coupling efficiency was obtained in coupling between thewaveguide mode of the SHG device 2 and the emission mode of thesemiconductor laser.

A mounting method is described with reference to FIGS. 8A to 8D.

In the first embodiment, glass beads were mixed with acetone, which wasstirred well. A trace amount of the material thus obtained was appliedto the optical waveguide formation surface of the SHG device. As aresult, a layer of the glass beads dispersed on the optical waveguideformation surface was formed. Afterwards, an ultraviolet curable agentwas applied to the Si submount, the position of the SHG device in theheight direction was adjusted, and then the SHG device was fixed to theSi submount. In the present embodiment, a method was employed as asimpler mounting method, in which the position of the optical waveguideQPM-SHG device 16 in the height direction was adjusted using an adhesiveprepared by mixing a plurality of glass beads 14 having a mean grainsize (φ) of 2.7 μm with an ultraviolet curable agent 13, and then theSHG device 16 was fixed to the Si submount 15.

In the present embodiment, an epoxy-based material obtained by cationicpolymerization was used as the ultraviolet curable agent. A trace amountof glass beads 14 was mixed with the ultraviolet curable agent, whichthen was stirred well. The ultraviolet curable agent 13 containing theglass beads 14 was applied to the Si submount 15 with awavelength-variable DBR semiconductor laser 17 mounted thereon. Theglass beads 14 were mixed with the ultraviolet curable agent 13 in aratio of about 10 vol. %, which was used in the present embodiment. Whenthe ratio of the glass beads 14 in the ultraviolet curable agent 13 isexcessively high, it is difficult to stir the glass beads 14 uniformlyand the ultraviolet curable agent 13 is applied to the submount 15 withglass beads 14 gathering together. Consequently, it may be difficult toarrange the glass beads 14 in a single layer in some cases. Therefore,it is desirable that the ratio of the glass beads 14 in the ultravioletcurable agent 13 does not exceed 30 vol. %.

In the first embodiment, the position of the SHG device 16 was adjustedso that a maximum optical coupling efficiency was obtained, while thesemiconductor laser was allowed to emit a beam. In the presentembodiment, the position adjustment was carried out by image processingusing markers M1 and M2 formed on the Si submount 15 and the SHG device16. Thus, a passive alignment mounting was carried out. Additionally,markers M3 were formed on the DBR semiconductor laser 17 and thus thesemiconductor laser 17 was fixed to the Si submount 15 with highprecision. The position accuracy by the image processing did not exceed±0.2 μm.

FIG. 8A explains the methods of adjusting and mounting the DBRsemiconductor laser 17. Two markers M3 on the semiconductor laser 17were detected and the midline between them was determined. Then, twomarkers M1 on the Si submount 15 were detected and the midline betweenthem also was determined. The position adjustment was carried out sothat the respective midlines coincided with each other. Then, a solder18 on the Si submount 15 was melted. Thus, the semiconductor laser 17was fixed to the Si submount 15.

As shown in FIG. 8B, the ultraviolet curable agent 13 containing glassbeads 14 mixed therewith was applied to the Si submount 15 with thesemiconductor laser 17 mounted thereon.

FIG. 8C explains the methods of adjusting and mounting the SHG device16. The SHG device was fixed to a vacuum pincette and was moved for theadjustment. Opposed end faces of the semiconductor laser 17 and theQPM-SHG device 16 were detected and the space therebetween was adjustedto be 3 μm. Then, two stripe markers M2 on the QPM-SHG device 16 weredetected and the midline between them was determined. At the same time,two markers M1 on the Si submount 15 also were detected and the midlinebetween them was determined. The position adjustment in the widthdirection was carried out so that the respective midlines coincide witheach other. Then, an irradiation of ultraviolet rays was conducted for30 seconds while a load was applied to the QPM-SHG device 16. Thus, theQPM-SHG device 16 was fixed to the Si submount 15 (FIG. 8D). In order toarrange the glass beads 14 in a single layer, it is required to apply aload to the QPM-SHG device 16. However, when the mounting is carried outunder a load of 500 g or more, the QPM-SHG device 16 may be damaged insome cases. Therefore, it is desirable that the load applied to theQPM-SHG device 16 does not exceed 500 g.

In order to control the gap between the Si submount 15 and the SHGdevice 16 with high precision, attention also should be paid to theposition where the load is applied. In order to control the gap betweenthe Si submount 15 and the SHG device 16 with high precision, the loadis required to be applied to a position located on the SHG device 16 andin the vicinity of the center of a region where the glass beads 14 areplaced, for the reason described in the first embodiment.

Furthermore, for the reason described in the first embodiment, it ispreferable that the area of a portion of a jig for applying a load tothe SHG device 16 coming into contact with the SHG device 16 is smallerthan the area of the SHG device 16.

In the present embodiment, the position adjustment in the heightdirection is made automatically by the glass beads. In addition, theposition adjustments in the optical axis direction and in the widthdirection were made through image processing by detecting the spacebetween opposed surfaces and the markers, respectively. With respect toa 50-mW semiconductor laser output, a 25-mW laser beam was coupled tothe optical waveguide. The wavelength of the DBR semiconductor laser wasallowed to coincide with the phase matched wavelength of the SHG device,so that 3-mW blue light with a wavelength of 410 nm was obtained. Themounting was completed with the same precision as that in the activealignment mounting. The configuration according to the presentembodiment also exhibits a significant practical effect in the passivealignment mounting.

Generally, the adhesive shrinks upon being cured. Therefore, when theadhesive is cured after the optical coupling adjustment, the opticalcoupling efficiency at the time of the adjustment differs from thatafter the fixing. In the present embodiment, however, glass beads arepresent between the SHG device and the Si submount. Therefore, themisalignment in the height direction is not caused even when theadhesive shrinks upon being cured. Thus, the configuration of thepresent embodiment has a significant practical effect.

The ultraviolet curable agent can be cured by irradiation of ultravioletrays. Therefore, the SHG device can be fixed in a short time byirradiation of ultraviolet rays after the optical coupling adjustment.Consequently, stable fixing is achieved. In the case of using athermosetting adhesive or the like, a shift in the position determinedby the optical coupling adjustment may occur during heating.Furthermore, in the substrate for a wavelength conversion deviceintended to generate blue light such as the Mg-doped LiNbO₃ substrate,since light in a wavelength range up to about 300 nm is transparent, theultraviolet curable agent is a preferable adhesive.

In the present embodiment, spherical glass beads were used. However, thesame effect also can be obtained in the case of using fiber-like(cylindrical) bodies. Furthermore, their diameter can be adjusted withhigher precision and therefore the fiber-like bodies are preferable. Forthe reason described in the first embodiment, it is desirable that thecylindrical bodies have a length of 10 μm to 100 μm.

In the present embodiment, the glass beads were used for the adjustmentin the height direction. Glass has poor thermal conductivity. For theSHG device, it is important to have temperature uniformity since thephase matching is satisfied by periodical polarization reversal. Theheat generated by the semiconductor laser is transmitted through the Sisubmount, and this causes nonuniformity in the temperature of the SHGdevice. When the glass beads with poor thermal conductivity areinterposed as in the present embodiment, the uniformity in temperatureof the SHG device can be maintained. Thus, high-efficiency wavelengthconversion can be achieved. This provides a significant effect.

In the present embodiment, the optical waveguide quasi-phase-matchedsecond harmonic generation (QPM-SHG) device produced on a Mg-dopedLiNbO₃ substrate was used as a planar optical waveguide device. In sucha blue light source, the power of the blue light obtained isproportional to the square of the power of a fundamental wave to becoupled. Therefore, the improvement in optical coupling efficiency isparticularly important. The configuration of the present embodimentcapable of obtaining highly stable optical coupling characteristics is apractical means and has a significant effect. In addition, since the Sisubmount and the SHG device are not in direct contact due to thepresence of the spherical or cylindrical bodies, the influence of theheat generation by the semiconductor laser is considerably small.Therefore, the uniformity in temperature is maintained in the SHGdevice. This provides a significant practical effect.

Third Embodiment

In the present embodiment, the description is directed to a mountingmethod used for manufacturing an optical waveguide device integratedmodule. A semiconductor laser and an optical waveguide device includingan optical waveguide formed at the surface of its substrate are mountedon a submount with an active layer and an optical waveguide formationsurface facing the submount, respectively. After the semiconductor laseris fixed to the submount, an adhesive is applied to the submount. Then,the adjustment of optical coupling between the semiconductor laser andthe optical waveguide device is carried out with the adhesive beingpresent between the optical waveguide and the submount. Afterward, theoptical waveguide device is fixed. In other words, the description isdirected to a method in which the optical coupling adjustment is carriedout with the adhesive applied to the Si submount prior to theadjustment. In the first embodiment, initially, the optical couplingadjustment was carried out. Next, the SHG device was moved upward in thedirection perpendicular to the Si submount, and then the adhesive wasapplied to the Si submount. Afterward, the SHG device was moved downwardin the direction perpendicular to the Si submount. Thus, the SHG devicewas mounted. In this process, however, the SHG device is required to bemoved downward onto the Si submount twice. Therefore, it takes a longertime for the mounting. The mounting method of the present invention isdescribed with reference to FIGS. 9A to 9C.

As described in the first embodiment, the distance from the Si submountto an emission center of the semiconductor laser is 5 μm. The waveguidemode of the fundamental wave in the optical waveguide QPM-SHG device hada full width at half maximum of 3 μm with respect to the thicknessdirection. The distance from the substrate surface to a position wherethe intensity of the transverse mode reached its peak was 2 μm. In orderto achieve the optical coupling with high efficiency, it is required toadjust the position of the SHG device in the height direction. As in thefirst embodiment, the size of spherical glass beads 22 was determined sothat a maximum optical coupling efficiency was obtained in couplingbetween the waveguide mode of the SHG device 2 and the emission mode ofthe semiconductor laser.

As in the second embodiment, spherical glass beads 22 with a grain sizeof 2.7 μm were mixed with an ultraviolet curable agent 21 in a ratio ofabout 10 vol. % and used in the present embodiment. When the ratio ofthe glass beads 22 in the ultraviolet curable agent 21 is excessivelyhigh, it is difficult to stir the glass beads 22 uniformly and thus theultraviolet curable agent 21 is applied to the submount 23 with glassbeads 22 gathering together. Consequently, it may be difficult toarrange the glass beads 22 in a single layer in some cases. Therefore,it is desirable that the ratio of the glass beads 22 in the ultravioletcurable agent 21 does not exceed 30 vol. %.

As shown in FIG. 9A, the ultraviolet curable agent 21 containing 2.7-μmspherical glass beads 22 mixed therewith was applied to the Si submount23 with a wavelength-variable DBR semiconductor laser 20 mountedthereon. Next, the optical coupling adjustment was carried out while thesemiconductor laser was allowed to emit a beam. As shown in FIG. 9B, anoptical waveguide QPM-SHG device 19 was placed on the Si submount 23with the DBR semiconductor laser 20 mounted thereon. The SHG device wasfixed to a vacuum pincette and was moved for the adjustment. In thepresent embodiment, the position adjustment in the height directionautomatically was made by the glass beads 22. Therefore, the adjustmentswere carried out with respect to the optical axis direction and thewidth direction. The space between the opposed end faces of thesemiconductor laser and the SHG device was set to be 3 μm. Theadjustment in the width direction was carried out so that a peak outputof a laser beam obtained from the emission end face of the opticalwaveguide was obtained while the semiconductor laser and the SHG devicewere moved relative to each other in the width direction. Then, anirradiation of ultraviolet rays was conducted for about 30 seconds whilea load was applied to the SHG device 19. Thus, the SHG device 19 wasfixed (FIG. 9C). It is necessary to apply a load to the SHG device 19 toarrange the glass beads 22 in a single layer. However, when the mountingis carried out under a load set to be 500 g or more, the SHG device 19may be damaged in some cases. Therefore, it is desirable that the loadapplied to the SHG device 19 does not exceed 500 g.

In order to control the gap between the Si submount 23 and the SHGdevice 19 with high precision, attention also should be paid to theposition where the load is applied. In order to control the gap betweenthe Si submount 23 and the SHG device 19 with high precision, the loadis required to be applied to a position located on the SHG device 19 andin the vicinity of the center of a region where the glass beads 22 areplaced, for the reason described in the first embodiment.

Furthermore, for the reason described in the first embodiment, it ispreferable that the area of a portion of a jig for applying a load tothe SHG device 19 coming into contact with the SHG device 19 is smallerthan the area of the SHG device 19.

With respect to a 50-mW semiconductor laser output, a 25-mW laser beamwas coupled to the optical waveguide. The wavelength of the DBRsemiconductor laser was allowed to coincide with the phase matchedwavelength in the SHG device, so that 3-mW blue light with a wavelengthof 410 nm was obtained.

As described above, in the mounting method used for manufacturing anoptical waveguide device integrated module of the present invention, theoptical coupling adjustment is simplified and thus the time required formounting is shortened considerably. Thus, the method has a significantpractical effect.

In the present embodiment, an ultraviolet curable agent with a viscosityof 20 cps was used. The SHG device was fixed to a vacuum pincette andwas moved for the adjustment. When the suction power of the vacuumpincette is lower than the pulling force produced by the viscosity ofthe adhesive, the SHG device cannot be moved. FIG. 10 shows the resultsobtained when an adhesive was applied between the SHG device and thesubmount and the SHG device was held by suction by the vacuum pincettefor movement. The horizontal axis indicates the viscosity of theadhesive and the vertical axis an moving error amount in the case wherethe SHG device was moved by 1 mm. When the viscosity was 100 cps orlower, the moving error amount was not more than 1 μm. When theviscosity reached around 1000 cps, a moving error amount was aboutseveral hundreds of micrometers. As a result, practically, a viscosityof 100 cps or lower is preferable for carrying out the positionadjustment of the SHG device after the application of an adhesive as inthe present embodiment. However, the viscosity of the adhesive dependson the SHG device and the suction power of a jig (the vacuum pincette inthe present embodiment). Therefore, the viscosity of usable adhesivescan be increased by the increases in the area subjected to suction andin suction power or by the strong fixing of the SHG device to a vacuumchuck or the like instead of the vacuum pincette.

Generally, the adhesive shrinks upon being cured. Hence, when theadhesive is cured after the optical coupling adjustment, the opticalcoupling efficiency at the time of the adjustment differs from thatafter the fixing. In the present embodiment, however, glass beads arepresent between the SHG device and the Si submount. Consequently, themisalignment in the height direction is not caused even when theadhesive shrinks upon being cured. Thus, the configuration of thepresent embodiment has a significant practical effect.

The ultraviolet curable agent can be cured by irradiation of ultravioletrays. Therefore, the SHG device can be fixed in a short time byirradiation of ultraviolet rays after the optical coupling adjustment.Consequently, stable fixing is achieved. In the case of using athermosetting adhesive or the like, a shift in the position determinedby the optical coupling adjustment may occur during heating.Furthermore, in the substrate for a wavelength conversion deviceintended to generate blue light such as the Mg-doped LiNbO₃ substrate,since light in a wavelength range up to about 300 nm is transparent, theultraviolet curable agent is a preferable adhesive.

In the present embodiment, spherical glass beads were used. However, thesame effect also can be obtained in the case of using fiber-like(cylindrical) bodies. Furthermore, their diameter can be adjusted withhigher precision and therefore the fiber-like bodies are preferable. Forthe reason described in the first embodiment, it is desirable that thecylindrical bodies have a length of 10 μm to 100 μm.

In the present embodiment, the adjustment in the height direction alsowas carried out using the glass beads. Glass has poor thermalconductivity. For the SHG device, it is important to have temperatureuniformity since the phase matching is satisfied by periodicalpolarization reversal. The heat generated by the semiconductor laser istransmitted through the Si submount and causes nonuniformity intemperature of the SHG device. When the glass beads with poor thermalconductivity are interposed as in the present embodiment, the uniformityin temperature of the SHG device can be maintained. Thus,high-efficiency wavelength conversion can be achieved and this providesa significant effect.

In the present embodiment, the optical waveguide quasi-phase-matchedsecond harmonic generation (QPM-SHG) device produced on a Mg-dopedLiNbO₃ substrate was used as a planar optical waveguide device. In sucha blue light source, the power of the blue light obtained isproportional to the square of the power of a fundamental wave to becoupled. Therefore, the improvement in optical coupling efficiency isparticularly important. The configuration of the present embodimentcapable of obtaining highly stable optical coupling characteristics is apractical means and provides a significant effect. In addition, sincethe Si submount and the SHG device are not in direct contact due to thepresence of the spherical or cylindrical bodies, the influence of theheat generation by the semiconductor laser is considerably small.Consequently, the temperature uniformity of the SHG device is maintainedin the SHG device and this provides a significant practical effect.

In the present embodiment, the space in the height direction between theSHG device and the submount can be adjusted automatically by the glassbeads interposed therebetween. Hence, optical coupling adjustments werecarried out with respect to the optical axis direction and the widthdirection. However, when the pulling force produced by the viscosity ofthe adhesive is set to be small, the SHG device can be moved not only anin-plane direction but also in the up-and-down direction (the heightdirection). Thus, the viscosity of the adhesive is set suitably, so thatoptical coupling adjustments can be carried out with high precision inthe optical axis, width, and height directions without using the glassbeads. Accordingly, high-efficiency optical coupling can be achieved.

Fourth Embodiment

In the present embodiment, the description is directed to a method ofcontrolling the position of an active layer of a semiconductor laserwith high precision. In the above-mentioned embodiments, it was intendedto improve the position accuracy in the height direction of an opticalwaveguide QPM-SHG device by using spherical or cylindrical bodies. Inthe present embodiment, spherical or cylindrical bodies are placedbetween a semiconductor laser and a submount, so that the distance fromthe submount surface to the position of the active layer (i.e. theposition corresponding to half the thickness of the active layer) in thesemiconductor laser is controlled with high precision. Thus,high-efficiency optical coupling is achieved.

FIG. 11 shows a SHG blue light source produced according to the presentinvention. The same wavelength-variable DBR semiconductor laser 3 as inthe embodiments described above is employed as a semiconductor laser inthe present embodiment. On a Si submount 4, a Ti/Pt/Au metallized filmis formed and a Pb/Sn solder 10 is formed by vacuum-evaporation in aportion on which the semiconductor laser is to be mounted. The thicknessof the solder material is 3 μm.

Conventionally, the position of the DBR semiconductor laser 3 in theheight direction was controlled by the adjustment of an amount ofpressure applied to the DBR semiconductor laser 3 during mounting. Thethickness of the solder 10 after the DBR semiconductor laser 3 was fixedwas set to be 2 μm. The actual accuracy in thickness of the solder 10was about ±0.2 μm.

Methods of reliably controlling the position of the DBR semiconductorlaser 3 in the height direction with higher precision include a methodusing spherical or cylindrical bodies with the same diameter as that ofthe spherical or cylindrical bodies used in the position control of theQPM-SHG device in the height direction. In the present embodiment,spherical glass beads were used. The mean grain size of the glass beads33 was set to be 2 μm. For the reason described in the first embodiment,it is desirable that the spherical bodies have a grain size of 10 μm orsmaller.

The glass beads 33 were placed between the DBR semiconductor laser 3 andthe submount 4 and then the solder 10 was melted while a load wasapplied to the DBR semiconductor laser 3. Thus, the DBR semiconductorlaser 3 was fixed to the submount 4. The glass beads 33 serve as astopper and thus the thickness of the solder 10 can be controlled withhigh precision. In order to control the gap between the DBRsemiconductor laser 3 and the Si submount 4 with high precision,attention also should be paid to the position where the load is applied.In order to control the gap between the Si submount 4 and the DBRsemiconductor laser 3 with high precision, the load is required to beapplied to a position located on the DBR semiconductor laser 3 and inthe vicinity of the center of a region where the glass beads 33 areplaced, for the reason described in the first embodiment.

Furthermore, for the reason described in the first embodiment, it ispreferable that the area of a portion of a jig for applying a load tothe DBR semiconductor laser 3 coming into contact with the DBRsemiconductor laser 3 is smaller than the area of the DBR semiconductorlaser 3.

As a result, the distance from the submount 4 to an active layer 8 ofthe DBR semiconductor laser 3 also can be controlled reliably with highprecision. The variation in mean grain size of the glass beads was ±0.1μm. Therefore, the thickness of the solder 10 was controlled with highprecision and thus the accuracy in thickness of the solder 10 wasimproved from ±0.2 μm to ±0.1 μm. The position of an optical waveguideQPM-SHG device in the height direction also was controlled using theglass beads 11 as in the embodiments described above. Then, the SHGdevice was mounted on the submount 4.

With respect to a 50-mW semiconductor laser output, an at least 25-mWlaser beam was coupled to an optical waveguide. The wavelength of theDBR semiconductor laser was allowed to coincide with a phase matchedwavelength in the SHG device. Thus, 3-mW blue light with a wavelength of410 nm was obtained. The thickness of the solder 10 was controlled withhigher precision as compared to a conventional case, so thathigh-efficiency optical coupling was achieved more stably and theimprovement in yield was confirmed.

The same result as in the above also can be obtained when the glassbeads 33 are premixed with the solder 10. When the ratio of the glassbeads 33 contained in the solder 10 is excessively high, it is difficultto distribute the glass beads 33 uniformly. In this case, the glassbeads 33 may be placed on the submount 16 in a gathered state and thusit may be difficult to arrange the glass beads 33 in a single layer insome cases. Therefore, it is desirable that the ratio of the glass beads33 in the solder 10 does not exceed 30 vol. %.

In the present embodiment, the solder was used as the adhesive forfixing the DBR semiconductor laser 3. However, a conductive adhesivealso may be used. The conductive adhesive is free from lead and thus hasless influence on the environment.

In the present embodiment, spherical glass beads were used. However, thesame effect also can be obtained in the case of using fiber-like(cylindrical) bodies. Their diameter can be adjusted with higherprecision and therefore the fiber-like bodies are preferable. For thereason described in the first embodiment, it is desirable that thecylindrical bodies have a length of 10 μm to 100 μm.

In the present embodiment, the optical waveguide quasi-phase-matchedsecond harmonic generation (QPM-SHG) device produced on a Mg-dopedLiNbO₃ substrate was used as a planar optical waveguide device. In sucha blue light source, the power of the blue light obtained isproportional to the square of the power of a fundamental wave to becoupled. Therefore, the improvement in optical coupling efficiency isparticularly important. The configuration of the present embodimentcapable of obtaining highly stable optical coupling characteristics is apractical means and provides a significant effect.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. An optical waveguide device integrated module,comprising: a semiconductor laser, including an active layer and asurface at which the active layer is formed; an optical waveguidedevice, including an optical waveguide formed on a substrate and asurface at which the optical waveguide is formed; and a submount,wherein the semiconductor laser and the optical waveguide device aremounted on the submount with both the surface at which the active layeris formed and the surface at which the optical waveguide is formedfacing the submount, and the submount is combined with the semiconductorlaser or the optical waveguide device to form one body using an adhesivewith a spacer being interposed therebetween, the spacer maintaining asubstantially uniform distance between the submount and thesemiconductor laser or the optical waveguide device, wherein the spaceris formed of at least one material selected from the group consisting ofglass, resins, and ceramics.
 2. The optical waveguide device integratedmodule according to claim 1, wherein the spacer is a spherical orcylindrical body.
 3. The optical waveguide device integrated moduleaccording to claim 2, wherein a relationship of d₁+d₂+Δ≅d₃+d₄ issatisfied, where d₁ denotes a diameter of the spherical or cylindricalbody, d₂ a distance from the surface of the optical waveguide device toa position where an intensity of a laser beam waveguide mode of theoptical waveguide reaches its peak, d₃ a distance from the surface ofthe semiconductor laser at which the active layer is formed to aposition where an intensity of an emission laser beam reaches its peak,d₄ a thickness of the adhesive used for mounting the semiconductor laseron the submount, and Δ a distance between the position where anintensity of a laser beam waveguide mode of the optical waveguidereaches its peak and a position where a maximum optical couplingefficiency is obtained in coupling a beam emitted from the semiconductorlaser to the optical waveguide.
 4. The optical waveguide deviceintegrated module according to claim 3, wherein Δ≅0 and Δ=α when thelaser beam waveguide mode of the optical waveguide has a symmetric shapeand an asymmetric shape with respect to a direction of a thickness ofthe substrate, respectively, where α denotes a distance between theposition where an intensity of a laser beam waveguide mode of theoptical waveguide reaches its peak and the position where a maximumoptical coupling efficiency is obtained in coupling a beam emitted fromthe semiconductor laser to the optical waveguide.
 5. The opticalwaveguide device integrated module according to claim 2, wherein thespherical body has a mean grain size of not more than 10 μm.
 6. Theoptical waveguide device integrated module according to claim 2, whereinthe cylindrical body has a mean length of 10 μm to 100 μm.
 7. Theoptical waveguide device integrated module according to claim 1, whereina size of the spacer is selected so that a maximum optical couplingefficiency is obtained in coupling a beam emitted from the semiconductorlaser to the optical waveguide.
 8. The optical waveguide deviceintegrated module according to claim 1, wherein a plurality of spacersare present.
 9. The optical waveguide device integrated module accordingto claim 8, wherein the plurality of spacers are arranged in a singlelayer between the optical waveguide device or the semiconductor laserand the submount.
 10. The optical waveguide device integrated moduleaccording to claim 8, wherein an amount of the plurality of spacersmixed with the adhesive is not more than 30 vol. %.
 11. The opticalwaveguide device integrated module according to claim 8, wherein theplurality of spacers have substantially the same size.
 12. The opticalwaveguide device integrated module according to claim 1, wherein thespacer is mixed with the adhesive.
 13. The optical waveguide deviceintegrated module according to claim 1, wherein the optical waveguidedevice is a quasi-phase-matched second harmonic generation device with aregion whose polarization is reversed periodically.
 14. The opticalwaveguide device integrated module according to claim 1, wherein theadhesive in the optical waveguide device is an ultraviolet ray curableadhesive.
 15. The optical waveguide device integrated module accordingto claim 1, wherein the adhesive used for fixing the semiconductor laseris a solder or a conductive adhesive.
 16. A method of manufacturing anoptical waveguide device integrated module comprising a semiconductorlaser and an optical waveguide device mounted on a submount with both asurface of the semiconductor laser at which an active layer is formedand a surface of the optical waveguide device at which an opticalwaveguide is formed facing the submount, the method comprising mountingat least one of the semiconductor laser and the optical waveguide deviceon the submount with an adhesive, with a spacer between the submount andthe semiconductor laser or the optical waveguide device, the spacermaintaining a substantially uniform distance between the submount andthe semiconductor laser or the optical waveguide device, wherein thespacer is a spherical or cylindrical body, and the spherical orcylindrical body is formed of at least one material selected from thegroup consisting of glass, resins, and ceramics.
 17. The method ofmanufacturing an optical waveguide device integrated module according toclaim 16, wherein at least one of the optical waveguide device and thesemiconductor laser is mounted on the submount while a load is appliedto the at least one.
 18. The method of manufacturing an opticalwaveguide device integrated module according to claim 17, wherein acenter position of the load is: in a vicinity of the plurality ofspacers when the plurality of spacers are positioned in one place; on aline extending between two points when the plurality of spacers arepositioned in two places; or inside a region defined by lines extendingbetween three points or more when the plurality of spacers arepositioned in three places or more; and on the optical waveguide deviceor the semiconductor laser.
 19. The method of manufacturing an opticalwaveguide device integrated module according to claim 17, wherein theload applied to the optical waveguide device is not more than 500 g. 20.The method of manufacturing an optical waveguide device integratedmodule according to claim 16, wherein a size of the spacer is selectedso that a maximum optical coupling efficiency is obtained in thecoupling between a beam emitted from the semiconductor laser and theoptical waveguide formed in the optical waveguide device.
 21. The methodof manufacturing an optical waveguide device integrated module accordingto claim 16, wherein a plurality of spacers are provided, and theplurality of spacers are arranged in a single layer between the opticalwaveguide device or the semiconductor laser and the submount.
 22. Themethod of manufacturing an optical waveguide device integrated moduleaccording to claim 21, wherein a ratio of the plurality of spacers mixedwith the adhesive is not more than 30 vol. %.
 23. The method ofmanufacturing an optical waveguide device integrated module according toclaim 21, wherein the plurality of spacers have substantially the samesize.
 24. The method of manufacturing an optical waveguide deviceintegrated module according to claim 16, wherein an area of a portion ofa jig used in mounting the at least one of the optical waveguide deviceand the semiconductor laser on the submount coming into contact with theoptical waveguide device or the semiconductor laser is smaller than anarea of the optical waveguide device or the semiconductor laser.
 25. Themethod of manufacturing an optical waveguide device integrated moduleaccording to claim 16, wherein the spacer is mixed with the adhesive.26. The method of manufacturing an optical waveguide device integratedmodule according to claim 16, wherein a position of the opticalwaveguide device is adjusted with the semiconductor laser emitting abeam and then the optical waveguide device is mounted on the submount.27. The method of manufacturing an optical waveguide device integratedmodule according to claim 16, wherein the optical waveguide device is aquasi-phase-matched second harmonic generation device with a regionwhose polarization is reversed periodically.
 28. The method ofmanufacturing an optical waveguide device integrated module according toclaim 16, wherein the adhesive is an ultraviolet curable agent.
 29. Themethod of manufacturing an optical waveguide device integrated moduleaccording to claim 16, wherein the spherical body has a mean grain sizeof not more than 10 μm.
 30. The method of manufacturing an opticalwaveguide device integrated module according to claim 17, wherein thecylindrical body has a mean length of 10 μm to 100 μm.
 31. The method ofmanufacturing an optical waveguide device integrated module according toclaim 16, wherein the adhesive is applied to the submount, an adjustmentin optical coupling between the semiconductor laser and the opticalwaveguide device is carried out with the adhesive being present betweenthe optical waveguide device and the submount, and then the opticalwaveguide device is fixed.
 32. An optical waveguide device integratedmodule, comprising: a semiconductor laser, including an active layer anda surface at which the active layer is formed; an optical waveguidedevice, including an optical waveguide formed on a substrate and asurface at which the optical waveguide is formed; and a submount,wherein the semiconductor laser and the optical waveguide device aremounted on the submount with both the surface at which the active layeris formed and the surface at which the optical waveguide is formedfacing the submount, and the submount is combined with the semiconductorlaser or the optical waveguide device to form one body using an adhesivewith a spacer being interposed therebetween, the spacer maintaining asubstantially uniform distance between the submount and thesemiconductor laser or the optical waveguide device, wherein the spaceris a spherical or cylindrical body, and the cylindrical body has a meanlength of 10 μm to 100 μm.
 33. The optical waveguide device integratedmodule according to claim 32, wherein a size of the spacer is selectedso that a maximum optical coupling efficiency is obtained in coupling abeam emitted from the semiconductor laser to the optical waveguide. 34.The optical waveguide device integrated module according to claim 32,wherein a plurality of spacers are present.
 35. The optical waveguidedevice integrated module according to claim 34, wherein the plurality ofspacers are arranged in a single layer between the optical waveguidedevice or the semiconductor laser and the submount.
 36. The opticalwaveguide device integrated module according to claim 34, wherein anamount of the plurality of spacers mixed with the adhesive is not morethan 30 vol. %.
 37. The optical waveguide device integrated moduleaccording to claim 34, wherein the plurality of spacers havesubstantially the same size.
 38. The optical waveguide device integratedmodule according to claim 32, wherein the spacer is mixed with theadhesive.
 39. The optical waveguide device integrated module accordingto claim 32, wherein a relationship of d₁+d₂+Δ≅d₃+d ₄ is satisfied,where d₁ denotes a diameter of the spherical or cylindrical body, d₂ adistance from the surface of the optical waveguide device to a positionwhere an intensity of a laser beam waveguide mode of the opticalwaveguide reaches its peak, d₃ a distance from the surface of thesemiconductor laser at which the active layer is formed to a positionwhere an intensity of an emission laser beam reaches its peak, d₄ athickness of the adhesive used for mounting the semiconductor laser onthe submount, and Δ a distance between the position where an intensityof a laser beam waveguide mode of the optical waveguide reaches its peakand a position where a maximum optical coupling efficiency is obtainedin coupling a beam emitted from the semiconductor laser to the opticalwaveguide.
 40. The optical waveguide device integraetd module accordingto claim 39, wherein Δ≅0 and Δ=α when the laser beam waveguide mode ofthe optical waveguide has a symmetric shape and an asymmetric shape withrespect to a direction of a thichkness of the substrate, respectively,where α denotes a distance between the position where an intensity of alaser beam waveguide mode of the optical waveguide reaches its peak andthe position where a maximum optical coupling efficiency is obtained incoupling a beam emitted from the semiconductor laser to the opticalwaveguide.
 41. The optical waveguide device integrated module accordingto claim 32, wherein the optical waveguide device is aquasi-phase-matched second harmonic generation device with a regionwhose polarization is reversed periodically.
 42. The optical waveguidedevice integrated module according to claim 32, wherein the spacer isformed of at least one material selected from the group consisting ofglass, resins, and ceramics.
 43. The optical waveguide device integratedmodule according to claim 32, wherein the adhesive in the opticalwaveguide device is an ultraviolet ray curable adhesive.
 44. The opticalwaveguide device integrated module according to claim 32, wherein theadhesive used for fixing the semiconductor laser is a solder or aconductive adhesive.
 45. The optical waveguide device integrated moduleaccording to claim 32, wherein the spherical body has a mean grain sizeof not more than 10 μm.
 46. A method of manufacturing an opticalwaveguide device integrated module comprising a semiconductor laser andan optical waveguide device mounted on a submount with both a surface ofthe semiconductor laser at which an active layer is formed and a surfaceof the optical waveguide device at which an optical waveguide is formedfacing the submount, the method comprising mounting at least one of thesemiconductor laser and the optical waveguide device on the submountwith an adhesive, with a spacer between the submount and thesemiconductor laser or the optical waveguide device, the spacermaintaining a substantially uniform distance between the submount andthe semiconductor laser or the optical waveguide device, wherein thespacer is a spherical or cylindrical body, and the cylindrical body hasa mean length of 10 μm to 100 μm.
 47. The method of manufacturing anoptical waveguide device integrated module according to claim 46,wherein at least one of the optical waveguide device and thesemiconductor laser is mounted on the submount while a load is appliedto the at least one.
 48. The method of manufacturing an opticalwaveguide device integrated module according to claim 47, wherein acenter position of the load is: in a vicinity of the plurality ofspacers when the plurality of spacers are positioned in one place; on aline extending between two points when the plurality of spacers arepositioned in two places; or inside a region defined by lines extendingbetween three points or more when the plurality of spacers arepositioned in three places or more; and on the optical waveguide deviceor the semiconductor laser.
 49. The method of manufacturing an opticalwaveguide device integrated module according to claim 47, wherein theload applied to the optical waveguide device is not more than 500 g. 50.The method of manufacturing an optical waveguide device integratedmodule according to claim 46, wherein a size of the spacer is selectedso that a maximum optical coupling efficiency is obtained in thecoupling between a beam emitted from the semiconductor laser and theoptical waveguide formed in the optical waveguide device.
 51. The methodof manufacturing an optical waveguide device integrated module accordingto claim 46, wherein a plurality of spacers are provided, and theplurality of spacers are arranged in a single layer between the opticalwaveguide device or the semiconductor laser and the submount.
 52. Themethod of manufacturing an optical waveguide device integrated moduleaccording to claim 51, wherein the plurality of spacers havesubstantially the same size.
 53. The method of manufacturing an opticalwaveguide device integrated module according to claim 46, wherein anarea of a portion of a jig used in mounting the at least one of theoptical waveguide device and the semiconductor laser on the submountcoming into contact with the optical waveguide device or thesemiconductor laser is smaller than an area of the optical waveguidedevice or the semiconductor laser.
 54. The method of manufacturing anoptical waveguide device integrated module according to claim 46,wherein the spacer is mixed with the adhesive.
 55. The method ofmanufacturing an optical waveguide device integrated module according toclaim 54, wherein a ratio of the plurality of spacers mixed with theadhesive is not more than 30 vol. %.
 56. The method of manufacturing anoptical waveguide device integrated module according to claim 46,wherein a position of the optical waveguide device is adjusted with thesemiconductor laser emitting a beam and then the optical waveguidedevice is mounted on the submount.
 57. The method of manufacturing anoptical waveguide device integrated module according to claim 46,wherein the optical waveguide device is a quasi-phase-matched secondharmonic generation device with a region whose polarization is reversedperiodically.
 58. The method of manufacturing mounting an opticalwaveguide device integrated module according to claim 46, wherein thespherical or cylindrical body is formed of at least one materialselected from the group consisting of glass, resins, and ceramics. 59.The method of manufacturing an optical waveguide device integratedmodule according to claim 46, wherein the adhesive is an ultravioletcurable agent.
 60. The method of manufacturing an optical waveguidedevice integrated module according to claim 46, wherein the sphericalbody has a mean grain size of not more than 10 μm.
 61. The method ofmanufacturing an optical waveguide device integrated module according toclaim 46, wherein the adhesive is applied to the submount, an adjustmentin optical coupling between the semiconductor laser and the opticalwaveguide device is carried out with the adhesive being present betweenthe optical waveguide device and the submount, and then the opticalwaveguide device is fixed.